This invention relates to anesthetic compositions, particularly to anesthetic compositions which can be applied using a pump dispenser. In particular, this invention is concerned with an anesthetic composition containing at least 10% benzocaine in a nonvolatile solvent, which composition additionally includes a diluent. The composition is designed for topical application and is characterized by being stable at room temperature and resistant to low temperatures, being relatively nonflammable, and being relatively inexpensive. The composition is designed for relief of surface pain and itching, and provides soothing temporary relief of minor burns, sunburn, cuts, scratches, nonpoisonous insect bites, poison ivy, and minor skin irritations.
Benzocaine is not completely effective as an anesthetic solution on the unbroken skin or mucous membranes at concentrations of less than 10%. In my U.S. Pat. No. 2,457,188, I disclose solutions containing 10% or more benzocaine dissolved in certain nonvolatile solvents. These nonvolatile solvents include aliphatic polyoxyalkylene glycols and aliphatic ethers of aliphatic dihydric alcohols which have a boiling point of not substantially less than 250.degree. C. and in which the ratio of the total number of aliphatic ether groups per molecule to the molecular weight of the compound is not less than 0.0033, and aromatic ethers of aliphatic dihydric alcohols, and carboxylic acid esters of aliphatic dihydric alcohols, and carboxylic acid esters of aromatic and aliphatic ethers of aliphatic dihydric alcohols which have a boiling point not substantially less than 250.degree. C. and in which the ratio of the total number of ether groups and ester groups per molecule to the molecular weight of the compound is not less than 0.0055. I disclose that these solutions may be subjected to much lower temperatures without precipitating any of the benzocaine. I also disclose that these solutions containing 10% or more benzocaine have superior anesthetic properties.
One convenient method of applying concentrated solutions of benzocaine has been by means of an aerosol employing a fluorocarbon. The fluorocarbon serves as a propellant for the anesthetic solution. In addition, it acts as a diluent to reduce the composition to a sprayable viscosity and to lower its cost (since fluorocarbons are less expensive than the anesthetic solutions). In my U.S. Pat. No. 3,322,624, I disclose aerosol anesthetic preparations having a high percentage of benzocaine and which are single phase systems and which are temperature resistant, being easily reconstitutable and/or adapted for use at low temperatures. These preparations include, as the solvent for the benzocaine, polyethylene glycol diesters represented by the formula: ##STR1## wherein n is an integer from 7 to 15 and R and R.sub.1 are alkyls containing from 7 to 11 carbons. These preparations also include a fluorocarbon such as dichlorodifluoromethane as the propellant, with the preparation containing at least 10% benzocaine in the solution (excluding the propellant) and at least one part by weight propellant to one part by weight of solvent.
Due to the danger that fluorocarbons pose to the ozone layer of the atmosphere because of the wide use of fluorocarbons in aerosol sprays, other means are being sought for applying anesthetic solutions. One such method is through the use of a pump dispenser. Use of a pump dispenser eliminates the need for a fluorocarbon propellant. However, a diluent for the anesthetic solution is required to lower the cost of the composition. The diluent, at the same time, reduces viscosity of the composition to a sprayable or more easily pumpable viscosity.
In choosing the diluent for the anesthetic solution to be applied using a pump dispenser, the stability of the solution must be considered. For example, many of the nonvolatile solvents for benzocaine are water soluble. However, when more than a minor amount of water is added as a diluent to solutions containing 10% or more benzocaine in one of these solvents, the solutions become unstable; benzocaine precipitates upon standing. Accordingly, water alone is not satisfactory as a diluent.
Moreover, alcohols such as isopropanol, n-propanol or ethanol produce stable, low viscosity solutions when used as diluents. However, these alcohols have a serious disadvantage; they produce a highly inflammable preparation that is dangerous to use.
In U.S. Pat. No. 2,097,687 to Curtis, solutions of anesthetics, such as benzocaine, in emollient vehicles, such as glycerine or castor oil, and alcohol, are made stable by including aspirin in approximately equal amounts with the benzocaine. The aspirin reacts with the benzocaine to form an acetyl salicylic acid salt of ethyl-para-amino benzoate. This composition, which includes alcohol, would be inflammable.
In U.S. Pat. No. 2,628,182 to Reasenberg, a liquid topical anesthetic composition having benzocaine in markedly high concentration is disclosed. The composition includes, in addition to benzocaine and propylene glycol, compounds derived from the interaction of a hexitan with lauric acid and an alkylene oxide, the alkylene oxide being either ethylene oxide or propylene oxide, with the number of moles of alkylene oxide being allowed to react per mole of hexitan being between eight and twenty-five.
In U.S. Pat. No. 3,624,224 to Wei et al., compositions including aqueous solutions of a germicidal quaternary ammonium compound, a local anesthetic, and a polyoxyethylene-polyoxypropylene block polymer are disclosed. These compositions can also include a humectant and dissolution-aiding material such as glycerine, propylene glycol, sorbitol, diethylene glycol, and polyethylene glycol, and a minor amount of isopropanol to impact a medicinal odor.